The influence of silicon on the structure and hardness of biomedical Ti–18Nb–4Zr–xSi alloys in as-cast state and after quenching

Keywords

biomedical Ti–Nb–Zr–Si alloys, structure, silicides, quenching, hardness.

Cite as

Shevchenko О. M., Kulak L. D., Kuzmenkо M. M., Kоtkо А. V., and Firstov S. O. The influence of silicon on the structure and hardness of biomedical Ti–18Nb–4Zr–xSi alloys in as-cast state and after quenching. Physico­chemical Mechanics of Materials. 2022. 58(2), 033-041.

Abstract

The biomedical Ti–18Nb–4Zr–хSi alloys with a silicon content of 0.5–1.5 wt.% were in­vestigated. Quenching in water was carried out in the temperature range of 900–1200°С with a holding time of 5 min and 1 h. Heating the as-cast alloys to quench temperatures leads to the disintegration of non-equilibrium phases; the silicon content is distributed between phases in the solid solution and silicides. Since almost all silicon binds to zirconium and titanium in silicides, the hardness of Ti–18Nb–4Zr–хSi alloys depends mainly on the quan­tity of silicides formed. The hardness of as-cast Ti–18Nb–4Zr–хSi alloys is 26–28 HRC and reaches the maximum values for the eutectoid composition of 0.8–1.2 wt.% Si, where the largest separation of disperse silicides takes place. The increase of silicon content in the hypereutectoid alloys leads to an increase in silicide sizes, as well to the formation of a greater amount of b-phase in the as-cast Ti–18Nb–4Zr–хSi alloys, and as a result, the hard­ness significantly decreases. At low quenching temperatures of 900–1000°C the complete eutectoid decomposition with the formation of relatively large, stable (Ti,Zr)₃Si silicides results in a reduction of hardness < 25 HRC. Quenching of the as-cast Ti–18Nb–4Zr–хSi alloys at the temperatures ≥ 1100°C causes the formation of dispersed silicides, which in­creases the hardness to 38–39 HRC in the alloys of eutectoid composition. Changes in the α”-phase parameters indicate that as a result of dissolution of a part of silicides on quen­ching at 1200°C silicon passes into a solid solution, while large silicides further increase at the boundaries of grains, and so the hardness of the quenched Ti–18Nb–4Zr–хSi alloys decreases.

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